Sealed secondary batteries include nickel metal hydride batteries, nickel cadmium batteries, and the like. Among of all, nonaqueous electrolyte secondary batteries typified by lithium ion batteries are small in weight and size and has high energy density, and are therefore employed in various usages as driving power supplies and backup power supplies for consumer-use appliances, such as mobile phones, electric vehicles, electric power tools and the like. Particularly, the nonaqueous electrolyte secondary batteries are becoming a focus of attention as the driving power supplies and the backup power supplies, and are under active development for increasing their capacity.
In order to increase the battery capacity, the electrode areas of the electrode assemblies may be increased by increasing the number of windings of the positive electrode and the negative electrode with the separator interposed therebetween, for example. However, as the number of windings is increased, the heat dissipation becomes worse, thereby leading to non-uniform temperature in the battery. This may causes shortening of the battery lifetime. In addition, an increased number of windings may cause a problem such as misaligned windings, and presents various manufacturing problems.
As a strategy for solving the above problems accompanied by upsizing of the batteries, Patent Document 1 discloses a method of accommodating an electrode assembly in a container with it separated into a plurality of small electrode assemblies.
FIG. 10 is a perspective view showing a configuration of a battery casing disclosed in Patent Document 1. As shown in FIG. 10, small electrode assemblies 102 each covered with a resin film 101 are accommodated in a container 103 partitioned by a plurality of metal-made partitions 104, so that heat generated at each electrode assembly 102 is released outside the container 103 effectively via the metal-made partitions 104.
However, the plurality of small electrode assemblies 102 accommodated in the container 13 are separated from one anther completely by the partitions 104. Therefore, upon occurrence of abnormality, for example, an uprush of gas or the like in some of the small electrode assemblies 102, the internal pressure of the part accommodating the small assembly 102 abruptly increases to cause the abnormally generated gas to jet out from the container 103.
To tackle this problem, Patent Document 2 discloses a method of communicating a plurality of compartments accommodating such small electrode assemblies to each other through communication paths.
FIG. 11 and FIG. 12 are sectional views showing a configuration of a battery casing disclosed in Patent Document 2. As shown in FIG. 11, the battery casing 201 accommodating a plurality of electrode assemblies is divided into accommodation parts 202, in which the electrode assemblies 203 are accommodated. Referring to a lid 204 arranged on top of the battery casing 201, as shown in FIG. 12, through holes 205 are formed in the vicinity of the boundaries of respective adjacent accommodation parts 202, and communication paths 206 for communicating the associated through holes 205 are formed in the upper part of the lid 204.
In the above configuration, since the accommodation parts 202 separated from one another share the spaces through the communication paths 206, gas generated at some most degraded electrode assembly 203 can be released to the other accommodation parts 202. This can balance the degradation degrees of the electrode assemblies 203 to prevent the lifetime of the battery as a whole from being shortened.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2000-348696    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2001-057199    Patent Document 3: Japanese Unexamined Patent Application Publication No. 2001-185225